Pile foundation and method of contructing pile foundation

ABSTRACT

The present invention relates to a pile foundation includes: a pile that extends in a vertical direction and that supports a tower structure, a pile head protruding above the ground, and a lower end of the pile being open; and a ground improving body that, in a state in which the pile has been driven into the ground, is provided inside the pile, and at least a part of the ground improving body being in close contact with an inner peripheral surface of the pile.

TECHNICAL FIELD

The present disclosure relates to a pile foundation and a method of constructing a pile foundation.

RELATED ART

Japanese Patent Application Laid-Open No. 2003-293938 discloses a structure in which a wind power generating device is constructed on a hollow monopile foundation. On the other hand, Japanese Patent Application Laid-Open No. S57-161224 discloses a pile foundation in which the area of the end face at the lower end of a steel pipe is increased by sandwiching cylindrical concrete at the inner peripheral surface at the lower end of the steel pipe pile.

SUMMARY OF INVENTION Problem to be Solved by the Invention

Incidentally, as a method of constructing a pile foundation such as a monopile foundation, a method of directly driving a pile into the ground by striking is known. By driving a pile into the ground, bearing capacity can be increased due to a tip blockage effect, and construction can be carried out in a short period of time. However, when the diameter of a pile is large, the tip blockage effect cannot be sufficiently obtained, and a large bearing capacity cannot be obtained. On the other hand, in a case in which the area of the end face of the lower end of a pile is increased as in Japanese Patent Application Laid-Open No. S57-161224, it becomes difficult for the pile to be driven into the ground and work efficiency decreases.

In consideration of the above facts, it is an object of the present disclosure to obtain a pile foundation and a method of constructing a pile foundation which can increase the bearing capacity of the pile while ensuring work efficiency.

Means for Solving the Problem

A pile foundation according to a first aspect includes: a pile that extends in a vertical direction and that supports a tower structure, a pile head protruding above the ground, and a lower end of the pile being open; and a ground improving body that, in a state in which the pile has been driven into the ground, is provided inside the pile, and at least a part of the ground improving body being in close contact with an inner peripheral surface of the pile.

In the pile foundation according to the first aspect, the ground improving body is provided inside the pile in a state in which the pile has been driven into the ground. Further, at least a part of the ground improving body is in close contact with the inner peripheral surface of the pile. Due thereto, a frictional force on the inner peripheral surface of the pile is improved at the portion at which the pile and the ground improving body are in close contact with each other. As a result, the bearing capacity of the pile can be increased.

Further, since the bearing capacity can be increased without increasing the thickness of the pile itself, the pile can be driven into the ground by striking.

In a pile foundation according to a second aspect, in the first aspect, sediment has entered inside the pile, and the ground improving body is provided between the inner peripheral surface of the pile and the sediment.

In the pile foundation according to the second aspect, by providing the ground improving body between the inner peripheral surface of the pile and the sediment, a construction period can be shortened as compared to a case in which the entirety of the sediment is used as the ground improving body.

In a pile foundation according to a third aspect, in the second aspect, the ground improving body is provided in plural locations, with spaces therebetween, along the inner peripheral surface of the pile in a cross-sectional view of the pile as viewed from an axial direction of the pile.

In the pile foundation according to the third aspect, a construction period can be shortened as compared to a case in which the ground improving body is provided across the entire circumference along the inner peripheral surface of the pile.

In a pile foundation according to a fourth aspect, in the second aspect or the third aspect, the ground improving body is formed only in a part, in an axial direction of the pile, of the sediment that has entered inside the pile.

In a pile foundation according to a fifth aspect, in the first aspect, the ground improving body is provided in an entire area inside the pile in a cross-sectional view of the pile as viewed from an axial direction of the pile.

In the pile foundation according to the fifth aspect, the rigidity of the entire inside portion of the pile can be improved by the ground improving body.

In a pile foundation according to a sixth aspect, in any one of the first aspect to the fifth aspect, the pile foundation is provided with a support member at the inner peripheral surface of the pile, in a vicinity of the pile head, the support member supporting the ground improving body from above.

In the pile foundation according to the sixth aspect, due to the ground improving body being supported from above by the support member, the pile and the ground improving body can be brought into close contact with each other and integrated.

A pile foundation according to a seventh aspect includes: a pile that extends in a vertical direction and that supports a tower structure, a pile head protruding above the ground, and a lower end of the pile being open; and a support member that is provided at an inner peripheral surface of the pile, in a vicinity of the pile head, the support member supporting, from above, at least a part of sediment that has entered inside the pile.

In the pile foundation according to the seventh aspect, the support member is provided at the inner peripheral surface of the pile, in a vicinity of the pile head, and at least a part of the sediment that has entered inside the pile is supported from above by the support member. By providing the support member in this manner, when the pile is driven into the ground, the sediment inside the pile can be compressed by the support member, and the tip blockage effect can be obtained.

In a pile foundation according to an eighth aspect, in the seventh aspect, the support member is a ring-shaped flange that extends toward a radial direction inner side from the inner peripheral surface of the pile.

In the pile foundation according to the eighth aspect, the sediment inside the pile can be compressed by the ring-shaped flange. Further, since the spaces above and below the flange are in communication with each other, it is possible to carry out ground improving by injecting a chemical agent or the like into the sediment after driving in the pile.

In a pile foundation according to a ninth aspect, in the seventh aspect, the support member is a disk-shaped member that blocks a lower end portion of the pile head.

In the pile foundation according to the ninth aspect, a vertical force can be transmitted to the entirety of the sediment inside the pile by the disk-shaped member.

In a pile foundation according to a tenth aspect, in any one of the seventh aspect to the ninth aspect, a filler is filled between the support member and the sediment that has entered inside the pile.

In the pile foundation according to the tenth aspect, the sediment and the support member can be integrated by the filler.

In a pile foundation according to an eleventh aspect, in any one of the first aspect to the tenth aspect, a floor slab is provided at the ground, and the floor slab is fixed to the pile head and transmits a force acting on the pile to the ground.

In the pile foundation according to the eleventh aspect, even in a case in which an external force is input in a falling down direction of the pile, at least a part of the external force can be transmitted to the ground via the floor slab, and a resistance force of the pile with respect to a horizontal force can be ensured.

In a pile foundation according to a twelve aspect, in any one of the first aspect to the eleventh aspect, the tower structure constitutes a leg portion of a wind power generating device.

In the pile foundation according to the twelfth aspect, even in a case in which a moment in a falling down direction acts on the pile due to a heavy object such as a wind power generating device, falling down of the pile can be suppressed by increasing the bearing capacity of the pile.

A method of constructing a pile foundation according to a thirteenth aspect, includes: a process of driving a pile into the ground, a lower end of the pile being open, such that a pile head protrudes above the ground; and a process of ground improving, of sediment that has entered inside the pile, at least a part of sediment that is in a vicinity of an inner peripheral surface of the pile.

In the method of constructing a pile foundation according to the thirteenth aspect, the ground improving body and the inner peripheral surface of the pile can be brought into close contact with each other by ground improving at least the sediment in the vicinity of the inner peripheral surface of the pile. As a result, a frictional force on the inner peripheral surface of the pile is improved, and the bearing capacity of the pile can be increased. Further, by driving the pile into the ground, it is possible to ensure work efficiency as compared with a method of constructing a pile after cutting the ground.

Effect of the Invention

As described above, by the pile foundation and the method of constructing a pile foundation according to the present disclosure, it is possible to increase the bearing capacity of a pile while ensuring work efficiency.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an overall view of a wind power generating device to which a pile foundation according to a first embodiment is applied.

FIG. 2A is a vertical cross-sectional view of a pile foundation according to the first embodiment.

FIG. 2B is a cross-sectional view showing a state of being cut along the line 2B-2B of FIG. 2A.

FIG. 3A is a vertical cross-sectional view of a pile foundation according to a modified example of the first embodiment.

FIG. 3B is a cross-sectional view showing a state of being cut along the line 3B-3B of FIG. 3A.

FIG. 4A is a vertical cross-sectional view of a pile foundation according to a second embodiment.

FIG. 4B is a cross-sectional view showing a state of being cut along the line 4B-4B of FIG. 4A.

FIG. 5A is a vertical cross-sectional view of a pile foundation according to a third embodiment.

FIG. 5B is a cross-sectional view showing a state of being cut along the line 5B-5B of FIG. 5A.

FIG. 6A is a vertical cross-sectional view of a pile foundation according to a fourth embodiment.

FIG. 6B is a cross-sectional view showing a state of being cut along the line 6B-6B of FIG. 6A.

FIG. 7A is a vertical cross-sectional view of a pile foundation according to a fifth embodiment.

FIG. 7B is a cross-sectional view showing a state of being cut along the line 7B-7B of FIG. 7A.

FIG. 8A is a vertical cross-sectional view of a pile foundation according to another example of the first embodiment.

FIG. 8B is a cross-sectional view showing a state of being cut along the line 8B-8B of FIG. 8A.

FIG. 9A is a vertical cross-sectional view of a pile foundation according to another example of the first embodiment.

FIG. 9B is a cross-sectional view showing a state of being cut along the line 9B-9B of FIG. 9A.

FIG. 10A is a schematic view showing a pressure bulb at the tip of a pile, which shows a pressure bulb at a small diameter pile.

FIG. 10B is a schematic view showing pressure bulbs at the tip of a pile, which shows pressure bulbs at a large diameter pile.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

A pile foundation 10 according to the first embodiment will be described with reference to the drawings. As shown in FIG. 1, the pile foundation 10 of the present embodiment is a foundation that supports a wind power generating device 12.

The wind power generating device 12 includes a leg portion (tower) 14 as a tower structure that extends in a vertical direction from the pile foundation 10, and a wind turbine 16 that is provided at the upper end portion of the leg portion 14. Further, the wind turbine 16 includes a nacelle 18, a hub 20, and blades 22.

The leg portion 14 of the wind power generating device 12 is formed such that the diameter of the leg portion 14 gradually decreases toward the upper side, and the lower end of the leg portion 14 is coupled to the pile foundation 10. Further, the nacelle 18 that constitutes the wind turbine 16 is rotatably attached to the upper end portion of the leg portion 14, and a generator and an amplifier (not shown) are housed inside the nacelle 18.

The nacelle 18 is coupled to the hub 20 via a rotor shaft (not shown). Plural blades 22, which are rotor blades, are attached to the hub 20, and in the present embodiment, as an example, three blades 22 are attached to the peripheral surface of the hub 20.

The leg portion 14 of the wind power generating device 12 configured as described above is supported by the pile foundation 10. Here, the pile foundation 10 of the present embodiment includes a substantially cylindrical pile 24.

The pile 24 is formed from a steel pipe and extends in the vertical direction, as an axial direction, and is provided substantially coaxially with the leg portion 14 of the wind power generating device 12. Further, the portion of the pile 24 excluding a pile head 24A that is provided at the upper part of the pile 24 is driven into the ground 26 by a striking method. Here, in the present embodiment, since the pile 24 is applied to the pile foundation 10 of an offshore wind power generating device 12, the pile 24 is driven into the seabed and is driven into a depth, from the ground 26, which is approximately 4 to 6 times the pile diameter of the pile 24. In the present embodiment, as an example, a pile 24 having a pile diameter of 5 to 9 m is used, and the pile 24 is driven into a depth of approximately 30 m from the ground 26.

As shown in FIG. 2A, the upper end and the lower end of the pile 24 are open, and by driving the pile 24 into the ground 26 by a striking method, sediment S enters inside the pile 24. By driving the pile 24 into the ground 26, the surface of the sediment S inside the pile 24 is located below the surface of the ground 26.

Here, in a state in which the pile 24 has been driven into the ground 26, a ground improving body 28 is provided inside the pile 24. As shown in FIG. 2B, the ground improving body 28 is provided such that at least a part thereof is in close contact with an inner peripheral surface 24B of the pile 24, and the ground improving body 28 of the present embodiment is provided between the inner peripheral surface 24B of the pile 24 and the sediment S.

Method of Constructing Pile Foundation

Next, an example of a method of constructing the pile foundation 10 of the present embodiment will be described. First, the pile 24 is driven into the ground 26 to a predetermined depth by a striking method. At this time, the pile 24 is driven in such that the pile head 24A protrudes above the ground 26. If a striking method is adopted in this manner, the pile 24 can be constructed on (driven into) not only sediment or relatively loose gravel ground, but also soft rock.

Subsequently, of the sediment S that has entered inside the pile 24, the sediment S that is in the vicinity of the inner peripheral surface 24B of the pile 24 is ground-improved. Specifically, plural injection holes are formed in the inner peripheral surface 24B of the pile 24, or inside the pile 24, in the axial direction of the steel pipe, an improving material such as a chemical agent or cement fine particles is injected at these injection holes from the upper part of the pile 24, and the ground improving body 28 is formed by infiltration injection. As another method, a boring hole is excavated from the upper part of the pile 24, and a ground improving material such as cement is injected by a stirring blade or jet injection to form the ground improving body 28. The pile foundation 10 is constructed in this manner.

Action

Next, the action of the present embodiment will be described.

In the pile foundation 10 of the present embodiment, at least a part of the ground improving body 28 is in close contact with the inner peripheral surface 24B of the pile 24. Thereby, the frictional force on the inner peripheral surface 24B of the pile 24 is improved at the portion at which the pile 24 and the ground improving body 28 are in close contact with each other. As a result, the bearing capacity of the pile 24 can be increased.

In particular, when the diameter of the pile 24 is large, a tip blockage effect cannot be sufficiently obtained and a large bearing capacity cannot be obtained; however, a large bearing capacity can be obtained by the structure of the present embodiment. This action will be described with reference to the model diagram of the pile shown in FIG. 10.

FIG. 10A shows a small-diameter pile 100. The diameter of the pile 100 is, for example, 1 m. In a case in which the pile 100 is driven into the ground 26 by a striking method, a pressure bulb with a strip load is formed by obtaining a tip blockage effect. The area T around the pile 100 is sediment which has been disturbed by the striking of the pile 100. In this manner, the apparent cross-sectional area of the pile 100 is increased such that the bearing capacity of the pile 100 is increased.

On the other hand, FIG. 10B shows a large-diameter pile 102. The diameter of the pile 102 is, for example, 5 to 9 m. In a case in which the pile 102 is driven into the ground 26 by a striking method, the width at which the sediment in the area T around the pile 102 is disturbed mainly depends on the ground. Further, since the sediment at the radial-direction center portion of the pile 102 is far from the peripheral surface of the pile 102, the sediment is not disturbed. For this reason, pressure bulbs with linear load are formed, and an increase in bearing capacity due to a tip blockage effect cannot be expected as compared with the small-diameter pile 100.

As described above, in a model such as in FIG. 10B, a tip blockage effect cannot be exerted beyond the frictional force on the inner peripheral surface of the pile 102, and it is considered that this tip blockage effect is almost equal to the frictional force on the inner peripheral surface of the pile 102. Here, assuming that the frictional force per unit area of the inner peripheral surface of the pile 102 is τ, the radius of the inner peripheral surface of the pile 102 is r_(in), and the height of the sediment that enters into the pile 102 is h, the total frictional force F is calculated by the following mathematical formula (1).

$\begin{matrix} {\left\lbrack {{Formula}\mspace{14mu} 1} \right\rbrack\mspace{619mu}} & \; \\ {F = {\tau \times 2\pi\; r_{in} \times h}} & (1) \end{matrix}$

On the other hand, assuming that the tip bearing capacity of the sediment at the inner peripheral surface of the pile 102 is P, and the bearing capacity per unit area is p_(in), the relationship between P and p_(in) is expressed by the following mathematical formula (2).

$\begin{matrix} {\left\lbrack {{Formula}\mspace{14mu} 2} \right\rbrack\mspace{619mu}} & \; \\ {P = {p_{in} \times \pi\; r_{in}^{2}}} & (2) \end{matrix}$

As described above, in the case in which the tip blockage effect is equal to the frictional force on the inner peripheral surface of the pile 102, the tip bearing force P and the total frictional force F are equal such that the following mathematical formula (3) holds true.

$\begin{matrix} {\left\lbrack {{Formula}\mspace{20mu} 3} \right\rbrack\mspace{619mu}} & \; \\ {{\tau \times 2\pi\; r_{i\; n} \times h} = {p_{i\; n} \times \pi\; r_{i\; n}^{2}}} & (3) \end{matrix}$

The following mathematical formula (4) is derived from the mathematical formula (3).

$\begin{matrix} {\left\lbrack {{Formula}\mspace{14mu} 4} \right\rbrack\mspace{619mu}} & \; \\ {p_{i\; n} = \frac{2\tau\; h}{r_{i\; n}}} & (4) \end{matrix}$

Looking at the above mathematical formula (4), it can be understood that the bearing capacity p_(in) per unit area at the inner peripheral surface of the pile 102 is inversely proportional to the radius r_(in) of the inner peripheral surface of the pile 102 _(in). That is, the larger the diameter of the pile 102, the smaller the bearing capacity of the tip.

On the other hand, according to the mathematical formula (4), it can be understood that by increasing the frictional force τ, the bearing capacity of the tip can be ensured even if the pile 102 has a large diameter. Here, in the present embodiment, as shown in FIG. 2A and FIG. 2B, the frictional force on the inner peripheral surface 24B of the pile 24 is increased by bringing the ground improving body 28 and the inner peripheral surface 24B of the pile 24 into close contact with each other. As a result, the bearing capacity of the pile 24 can be increased even in the case in which a pile 24 having a large diameter is used.

Further, in the present embodiment, since the bearing capacity can be increased without increasing the thickness of the pile 24 itself, the pile 24 can be driven into the ground 26 by striking. That is, it is not necessary to cut the ground 26 and then construct the pile. As a result, the bearing capacity of the pile 24 can be increased while ensuring work efficiency. In particular, in the case in which the pile foundation 10 is constructed at sea, a compact pile 24 can be used by adopting a configuration in which the bearing capacity is increased by the ground improving body 28 as in the present embodiment, and the specifications of a marine vessel for transportation can be downgraded. As a result, the cost of construction can be reduced.

Further, in the present embodiment, by providing the ground improving body 28 between the inner peripheral surface 24B of the pile 24 and the sediment S, the construction period can be shortened compared to a case in which the entirety of the sediment S is used as the ground improving body.

In the present embodiment, as shown in FIG. 2B, the ground improving body 28 is provided across the entire circumference of the inner peripheral surface 24B of the pile 24; however, the present disclosure is not limited to this. For example, the configuration of the modified example shown in FIGS. 3 may be adopted.

Modified Example

As shown in FIG. 3A, in the pile 24 that constitutes the pile foundation 30 of this modified example, the portion of the pile 24 excluding the pile head 24A that is provided at the upper part of the pile 24 is driven into the ground 26 by a striking method in a similar manner to as in the present embodiment.

Here, as shown in FIG. 3B, in a state in which the pile 24 has been driven into the ground 26, the ground improving body 28 is provided inside the pile 24. The ground improving body 28 is provided between the inner peripheral surface 24B of the pile 24 and the sediment S. Further, a ground improving body 31 is provided at plural locations, with spaces therebetween, along the inner peripheral surface 24B of the pile 24 in a cross-sectional view of the pile 24 as viewed from the axial direction of the pile 24, and in the present modified example, the ground improving body 31 is provided at five locations, with spaces therebetween, along the inner peripheral surface 24B.

As described above, in the present modified example, the frictional force can be increased at the portion at which the ground improving body 31 and the inner peripheral surface 24B of the pile 24 are in close contact with each other. Further, by providing the ground improving body 31 at plural locations, with spaces therebetween, along the inner peripheral surface 24B of the pile 24, the construction period can be shortened compared to a case in which a ground improving body is provided across the entire circumference along the inner peripheral surface 24B of the pile 24.

Second Embodiment

Next, a pile foundation 32 according to the second embodiment will be described with reference to FIG. 4A and FIG. 4B. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

As shown in FIG. 4A, the pile 24 that constitutes the pile foundation 32 of the present embodiment is configured in a similar manner to as in the first embodiment. The portion of the pile 24 excluding the pile head 24A is driven into the ground 26 by a striking method.

Here, a ground improving body 33 is provided inside the pile 24. The ground improving body 33 is provided such that at least a part thereof is in close contact with the inner peripheral surface 24B of the pile 24, and the ground improving body 33 of the present embodiment is provided in the entire area inside the pile 24 in a cross-sectional view of the pile 24 as viewed from the axial direction of the pile 24.

Further, the inner peripheral surface 24B of the pile 24 is provided with a flange 34 as a support member that partitions the internal space of the pile 24 into an upper space and a lower space, and supports the ground improving body 33 from above. The flange 34 is made of metal and is disposed in the vicinity of the pile head 24A, and is joined (fixed) to the inner peripheral surface 24B of the pile 24 by welding or the like.

Further, the flange 34 extends radially inward from the inner peripheral surface 24B of the pile 24 and is formed in a ring shape, and as shown in FIG. 4B, a substantially circular opening 34A is formed in the radial center portion of the flange 34. As a result, the ground improving body 33 is exposed to the pile head 24A side through the opening 34A.

Here, an example of the method of constructing the pile foundation 32 of the present embodiment will be described. First, the flange 34 is joined to the inner peripheral surface 24B of the pile 24. Then, the pile 24 provided with the flange 34 is driven into the ground 26 to a predetermined depth by a striking method. At this time, the pile head 24A is made to protrude above the ground 26.

Subsequently, the ground improving body 33 is formed by ground improving the entirety of the sediment that has entered inside the pile 24. The pile foundation 10 is constructed in this manner.

Action

Next, the action of the present embodiment will be described.

In the pile foundation 32 of the present embodiment, the rigidity of the entire inside of the pile 24 can be improved by the ground improving body 33 that is provided in the entire area inside the pile 24. Further, due to the ground improving body 33 being supported from above by the flange 34, the pile 24 and the ground improving body 33 can be brought into close contact with each other and integrated.

Further, in the present embodiment, due to the flange 34 being formed in a ring shape, the sediment inside the pile 24 can be compressed by the flange 34. Furthermore, since the spaces above and below the flange 34 are in communication with each other, it is possible to carry out ground improving by injecting a chemical agent or the like into the sediment after driving in the pile 24. Other actions are similar to as in the first embodiment.

Third Embodiment

Next, a pile foundation 40 of the third embodiment will be described with reference to FIG. 5A and FIG. 5B. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

As shown in FIG. 5A, the pile 24 that constitutes the pile foundation 40 of the present embodiment is configured in a similar manner to as in the first embodiment. The portion of the pile 24 excluding the pile head 24A is driven into the ground 26 by a striking method.

Further, in a state in which the pile 24 has been driven into the ground 26, a ground improving body 28 is provided inside the pile 24. The ground improving body 28 is provided between the inner peripheral surface 24B of the pile 24 and the sediment S.

Here, in the present embodiment, a floor slab 42 is provided at the pile head 24A of the pile 24, and the floor slab 42 includes a base 42A and triangular plates 42B.

The base 42A is formed with the axial direction (vertical direction) of the pile 24 as the thickness direction, and is installed on the ground 26. Further, as shown in FIG. 5B, the base 42A is formed in a substantially circular shape concentric with the pile 24 in plan view. Further, in the present embodiment, as an example, the base 42A is formed from a steel material and is fixed to the peripheral surface of the pile head 24A. As a method of fixing the base 42A to the pile head 24A, in addition to welding, a method of mechanically fastening with bolts, nuts or the like may be adopted.

Plural triangular plates 42B are provided at the upper surface side of the base 42A. Eight triangular plates 42B are provided at equal intervals along the circumferential direction of the pile 24. Further, as shown in FIG. 5A, each of the triangular plates 42B is formed in a substantially triangular shape such that the direction along the pile 24 and the direction along the base 42A are linear portions.

The lower end surfaces of the triangular plates 42B extend in the radial direction of the pile 24 along the base 42A and are fixed to the upper surface of the base 42A. Further, the side surfaces of the triangular plates 42B, which are located at the center side of the pile 24, extend in a vertical direction along the pile head 24A and are fixed to the pile head 24A. As a method of fixing the triangular plates 42B to the base 42A and the pile head 24A, in addition to welding in a similar manner as for base 42A, a method of mechanically fastening with bolts, nuts or the like may be adopted.

As described above, the floor slab 42 is installed on the ground 26 and is fixed to the pile head 24A. As a result, the external force acting on the pile 24 is configured to be transmitted to the ground 26 via the floor slab 42.

Action

Next, the action of the present embodiment will be described.

In the pile foundation 40 of the present embodiment, even in a case in which an external force is input in a falling down direction of the pile 24, at least a part of this external force can be transmitted to the ground 26 via the floor slab 42, and a resistance force of the pile 24 with respect to a horizontal force can be ensured. In addition, the floor slab 42 can suppress scouring of the seabed. Other actions are similar to as in the first embodiment.

Fourth Embodiment

Next, a pile foundation 50 of the fourth embodiment will be described with reference to FIG. 6A and FIG. 6B. The same components as those in the second embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

As shown in FIG. 6A, in the pile foundation 50 of the present embodiment, the floor slab 42 described in the third embodiment is attached to the configuration of the second embodiment. Specifically, the ground improving body 33 is provided inside the pile 24, and the ground improving body 33 is provided in the entire area inside the pile 24 in a cross-sectional view of the pile 24 as viewed from the axial direction of the pile 24.

Further, the flange 34 is provided at the inner peripheral surface 24B of the pile 24. The flange 34 is disposed in the vicinity of the pile head 24A and is joined to the inner peripheral surface 24B of the pile 24 by welding or the like.

Furthermore, the floor slab 42 is provided at the pile head 24A of the pile 24, and the base 42A and the triangular plates 42B, which constitute the floor slab 42, are fixed to the pile head 24A.

Action

Next, the action of the present embodiment will be described.

In the pile foundation 50 of the present embodiment, in a similar manner to as in the third embodiment, even in a case in which an external force is input in a falling down direction of the pile 24, at least a part of this external force is transmitted to the ground 26 via the floor slab 42, and a resistance force of the pile 24 with respect to a horizontal force can be ensured. Other actions are similar to as in the first embodiment.

Fifth Embodiment

Next, a pile foundation 60 of the fifth embodiment will be described with reference to FIG. 7A and FIG. 7B. The same components as those in the first embodiment are designated by the same reference numerals, and the description thereof will be omitted as appropriate.

As shown in FIG. 7A, the pile 24 that constitutes the pile foundation 70 of the present embodiment is configured in a similar manner to as in the first embodiment. The portion of the pile 24 excluding the pile head 24A is driven into the ground 26 by a striking method.

Here, the inner peripheral surface 24B of the pile 24 is provided with a disk-shaped member 62 as a support member that partitions the internal space of the pile 24 into an upper space and a lower space, and supports the sediment S from above. The disk-shaped member 62 is disposed in the vicinity of the pile head 24A, and a peripheral edge portion of the disk-shaped member 62 is joined (fixed) to the inner peripheral surface 24B of the pile 24 by welding or the like.

Further, a filler 64 is filled between the sediment S that has entered inside the pile 24 and the disk-shaped member 62. As the filler 64, for example, mortar, concrete, fiber reinforced concrete, gypsum, grout, and fiber reinforced resin can be used. Further, the sediment S and the disk-shaped member 62 are integrated by the filler 64.

Action

Next, the action of the present embodiment will be described.

In the pile foundation 60 of the present embodiment, the disk-shaped member 62 is provided at the inner peripheral surface of the pile in the vicinity of the pile head 24A, and the sediment S that has entered inside the pile 24 is supported from above by the disk-shaped member 62. By providing the disk-shaped member 62 in this manner, when the pile 24 is driven into the ground 26, the sediment S inside the pile 24 can be compressed by the disk-shaped member 62, and a tip blockage effect can be obtained.

In particular, in the present embodiment, a vertical force can be transmitted by the disk-shaped member 62 to the entirety of the sediment S inside the pile 24 such that the bearing capacity of the pile 24 can be increased.

Further, in the present embodiment, the sediment S and the disk-shaped member 62 are integrated by the filler 64. As a result, the bearing capacity of the pile 24 can be increased without ground improving the sediment S inside the pile 24, as compared with the configuration in which the filler 64 is not provided.

Although the first to fifth embodiments and the modified examples have been described above, needless to say that the present disclosure can be implemented in various modes within a scope that does not depart from the gist of the present disclosure. For example, a configuration in which the above embodiments are combined may be adopted. That is, the flange 34 of the second embodiment shown in FIG. 4A and FIG. 4B may be fixed to the pile foundation 10 of the first embodiment shown in FIG. 2A and FIG. 2B. Further, the filler 64 of the fifth embodiment shown in FIG. 7A may be provided between the flange 34 and the ground improving body 33 of the second embodiment.

Further, although a metal flange 34 is provided at the inner peripheral surface 24B of the pile 24 in the above second embodiment and fourth embodiment, the present disclosure is not limited to this. For example, a flange made of concrete may be provided. In this case, the flange may be put in place after the pile 24 has been driven into the ground 26. Further, a filler such as grout may be filled between the flange and the sediment or the ground improving body.

Further, although the pile 24 is formed of a steel pipe in the above embodiments, the material of the pile 24 is not particularly limited, and the pile 24 may be formed of another material. For example, a wooden pile made of wood or a concrete pile made of concrete may be used. Furthermore, a pile which is a combination of these materials may be used.

In addition, although a pile foundation that supports the leg portion 14 of the wind power generating device 12 as a tower structure is described in the above embodiments, the present disclosure is not limited to this. That is, a pile foundation that supports another type of tower structure may be applied, or a pile foundation that supports a tower structure such as a steel tower may be applied. In this case, plural piles may be driven into the ground to support a tower structure such as a steel tower.

Further, in the first embodiment, as shown in FIG. 2, the ground improving body 28 is formed in the entire area in the axial direction with respect to the sediment S that has entered inside the pile 24; however, the present disclosure is not limited to this. For example, the configurations shown in FIG. 8 and FIG. 9 may be adopted.

As shown in FIG. 8A, in the pile foundation 70, the ground improving body 28 is provided inside the pile 24 in a state in which the pile 24 has been driven into the ground 26. Here, the ground improving body 28 is formed only in a part, in the axial direction, of the sediment S that has entered inside the pile 24. Further, as shown in FIG. 8B, the ground improving body 28 is provided between the inner peripheral surface 24B of the pile 24 and the sediment S.

Further, in the pile foundation 80 shown in FIG. 9A, the ground improving body 31 is provided in the pile 24, and the ground improving body 31 is formed only in a part, in the axial direction, of the sediment S that has entered inside the pile 24. Further, as shown in FIG. 9B, the ground improving body 31 is provided at plural locations, with spaces therebetween, along the inner peripheral surface 24B of the pile 24 in a cross-sectional view of the pile 24 as viewed from the axial direction of the pile 24, and in the present modified example, the ground improving body 31 is provided at five locations, with spaces therebetween, along the inner peripheral surface 24B.

The disclosures of Japanese Patent Application No. 2019-082270 are incorporated herein by reference in their entirety.

All documents, patent applications, and technical standards described herein are incorporated by reference herein to the same extent as if the individual documents, patent applications, and technical standards were specifically and individually described. 

1. A pile foundation comprising: a pile that extends in a vertical direction and that supports a tower structure, a pile head protruding above the ground, and a lower end of the pile being open; and a ground improving body that, in a state in which the pile has been driven into the ground, is provided inside the pile, and at least a part of the ground improving body being in close contact with an inner peripheral surface of the pile.
 2. The pile foundation according to claim 1, wherein: sediment has entered inside the pile; and the ground improving body is provided between the inner peripheral surface of the pile and the sediment.
 3. The pile foundation according to claim 2, wherein the ground improving body is provided in a plurality of locations, with spaces therebetween, along the inner peripheral surface of the pile in a cross-sectional view of the pile as viewed from an axial direction of the pile.
 4. The pile foundation according to claim 2, wherein the ground improving body is formed only in a part, in an axial direction of the pile, of the sediment that has entered inside the pile.
 5. The pile foundation according to claim 1, wherein the ground improving body is provided in an entire area inside the pile in a cross-sectional view of the pile as viewed from an axial direction of the pile.
 6. The pile foundation according to claim 1, wherein a support member is provided at the inner peripheral surface of the pile, in a vicinity of the pile head, the support member supporting the ground improving body from above.
 7. A pile foundation comprising: a pile that extends in a vertical direction and that supports a tower structure, a pile head protruding above the ground, and a lower end of the pile being open; and a support member that is provided at an inner peripheral surface of the pile, in a vicinity of the pile head, the support member supporting, from above, at least a part of sediment that has entered inside the pile.
 8. The pile foundation according to claim 7, wherein the support member is a ring-shaped flange that extends toward a radial direction inner side from the inner peripheral surface of the pile.
 9. The pile foundation according to claim 7, wherein the support member is a disk-shaped member that blocks a lower end portion of the pile head.
 10. The pile foundation according to claim 7, wherein a filler is filled between the support member and the sediment that has entered inside the pile.
 11. The pile foundation according to claim 1, wherein a floor slab is provided at the ground, and the floor slab is fixed to the pile head and transmits a force acting on the pile to the ground.
 12. The pile foundation according to claim 1, wherein the tower structure constitutes a leg portion of a wind power generating device.
 13. A method of constructing a pile foundation, the method comprising: a process of driving a pile into the ground, a lower end of the pile being open, such that a pile head protrudes above the ground; and a process of ground improving, of sediment that has entered inside the pile, at least a part of sediment that is in a vicinity of an inner peripheral surface of the pile. 